1. Field of the Invention
This invention relates to a flat earth terminal which is mounted on a printed circuit board incorporated in a chassis of an electronic apparatus, so as to electrically connect the printed circuit board and the chassis, and a method of surface-mounting the flat earth terminal onto the printed circuit board.
2. Description of the Related Art
In electronic apparatuses of various types, it is necessary to stabilize the reference potential of a printed circuit board incorporated in a chassis, by connecting an earth line of the printed circuit board to the chassis. For such earthing, exclusively an earth terminal designed to be surface-mounted on the printed circuit board and screwed to the chassis with the printed circuit board is used.
A typical example of this type of the earth terminal is disclosed in Japanese Patent No. 2863981, for example. The earth terminal disclosed therein comprises a plate-like main part with a screw insertion hole (round hole) in the center, and leg-like terminal parts continuously extending from an end of the main part. The terminal parts are portions intended to be soldered to the printed circuit board. The earth terminal of this particular structure is called a flat earth terminal.
The flat earth terminal is surface-mounted onto the printed circuit board exclusively by soldering the flat earth terminal to conductive sections provided on the printed circuit board in advance. Specifically, the surface-mounting of the flat earth terminal is carried out as follows: On the printed circuit board, in a region in which the earth terminal is to be mounted, conductive sections are provided in advance to correspond to the leg-like terminal parts, and also to corners of the main part, as necessary; Then, the terminal parts and perhaps also corners of the main part of the flat earth terminal placed on the printed circuit board are soldered to the conductive sections.
In the surface-mounting, however, sometimes solder flows to between the main part of the flat earth terminal and the printed circuit board. If solder flows up to a region surrounding the screw insertion hole of the main part of the earth terminal, which region is referred to as a “screwing region”, the state of contact between the earth terminal and the printed circuit board in the screwing region changes with a temporal change of the solder, which damages the effect of earthing using this earth terminal.
In the earth terminal (lug terminal) disclosed in the above-mentioned Japanese Patent, the terminal parts (leads) have end portions bent into a chevron shape. Thus, melted solder flows to under the chevron-shaped portions, but does not get under the main part (rectangular part) of the earth terminal. Consequently, the earth terminal is prevented from being raised by the solder getting under the main part.
However, since this earth terminal has chevron-shaped portions, if the chevron-shaped portions are formed with low accuracy, the earth terminal cannot be kept in a horizontal position but takes a tilted position. This causes problems such that the earth terminal is not sucked by a chip mounter in a good manner in the surface-mounting process, and that the chevron-shaped portions protruding upward obstruct the chip mounter's sucking operation. Further, when the flat earth terminal and its position should be recognized in an image formed by a camera, it is difficult to focus the camera on the flat earth terminal. Further, when the earth terminal is mounted on the side of a printed circuit board which faces a chassis, it is difficult to bring the main part in close contact with the chassis.
Publication DE-A-3101031 also discloses an earth terminal comprising a main part with a screw insertion hole and leg-like terminal parts (5). However, the leg-like terminal parts (5) are each passed through a hole in a circuit board and soldered to a conductor on the circuit board. Thus, this earth terminal anticipates a basically different manner of soldering than a Surface-mounted type earth terminal to which the present invention relates. Publication U.S. Pat. No. 5,395,350 discloses a terminal with a recess formed between a main part and a terminal part to prevent solder from flowing from the terminal part to the main part. However, this terminal belongs to a technique concerning a connector, and is irrelevant to a technique for surface-mounting on a printed circuit board to which the present invention relates.